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    <title>Help On LaTeX Modes</title>

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<h2>Modes</h2>


<p>When LaTeX is processing your input text, it is always in one of three

    modes:</p>


<ul>

    <li><i>Paragraph</i> mode</li>

    <li><i>Math</i> mode</li>

    <li><i>Left-to-right</i> mode, called LR mode for short</li>

</ul>


<p>LaTeX changes mode only when it goes up or down a staircase to a

    different level, though not all level changes produce mode changes.

    Mode changes occur only when entering or leaving an environment, or

    when LaTeX is processing the argument of certain text-producing

    commands. </p>


<h3>Paragraph mode</h3>


<p>Paragraph mode is the most common; it's the one LaTeX is in when

    processing ordinary text. In that mode, LaTeX breaks your text into

    lines and breaks the lines into pages. </p>


<p>There

    are also several text-producing commands and environments for making a

    box that put LaTeX in paragraph mode. The box made by one of these

    commands or environments will be called a

    <a href="ltx-294.html">parbox</a>. When LaTeX is in

    paragraph mode while making a box, it is said to be in inner paragraph

    mode. The normal paragraph mode, in which LaTeX starts out, is called

    outer paragraph mode.</p>


<h3>Math mode</h3>


<p>LaTeX is in math mode when it's generating a mathematical formula. It is

    in math mode in the <a href="ltx-115.html#math">math</a>,

    <a href="ltx-421.html">displaymath</a>, <a href="ltx-224.html">equation</a>,

    and <a href="ltx-223.html"> eqnarray</a> environments.</p>


<p>In math mode letters are assumed to be math symbols and spaced accordingly.

    Spaces in the input are ignored, except that spaces may be needed to

    delineate the end of commands.</p>


<h3>LR mode</h3>


<p>In LR mode, as in paragraph

    mode, LaTeX considers the output that it produces to be a string of

    words with spaces between them. In LR mode, unlike paragraph and math modes,

    spaces are not ignored; an input space creates an output space.

    However, unlike paragraph mode, LaTeX

    keeps going from left to right; it never starts a new line in LR mode.

    Even if you put a hundred words into an

    <tt><a href="ltx-265.html">\mbox</a></tt>, LaTeX would keep

    typesetting them from left to right inside a single box, and then

    complain because the resulting box was too wide to fit on the line.</p>


<p>LaTeX is in LR mode when it starts making a box with an

    <tt><a href="ltx-265.html">\mbox</a></tt> command.

    You can get it to enter a different mode inside the box - for example,

    you can make it enter math mode to put a formula in the box. </p>


<hr noshade="noshade" size="1">


<p>Also see <a href="ltx-115.html">Math Formulas</a><br>

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